The anticarcinogenic activity of green tea has been demonstrated in many epidemiological, animal and cell culture studies. The main green tea polyphenols (GTPs) in brewed green tea (GT) responsible for the health benefits are epigallocatechin gallate (EGCG) and epigallocatechin (EGC), with smaller amounts of epicatechin (EC) and epicatechin gallate (ECG). Their limited bioavailability and high metabolism (conjugation and methylation) may decrease the potential of GT in chemoprevention. We determined that 50 percent or more of GTPs in human prostate tissue and urine is found in methylated form and that methylation significantly decreased the anticarcinogenic activity of EGCG. Catechol-O-methyltransferase (COMT) is the enzyme responsible for methylation of polyphenols with a catechol structure. Catechol-compounds such as EGCG and quercetin, a natural flavonoid occurring in many fruits and vegetable, inhibit COMT activity in prostate cancer cells (LNCaP). Co-treatment of quercetin and EGCG enhanced the COMT inhibitory effect, decreased EGCG methylation and increased EGCG bioavailability significantly. Therefore it is our hypothesis that co-treatment with quercetin and green tea will increase the chemopreventive activity of GT by inhibiting EGCG methylation and increasing the bioavailability in prostate cancer (CaP). We will test our hypothesis and investigate the mechanism using two different mouse models: A) by treating severe combined immunodeficient (SCID) mice inoculated with LNCaP xenograft tumors with green tea (GT) alone, GT and 0.2% quercetin (Q)-diet, GT+0.4%Q-diet, 0.2%Q-diet alone, 0.4%Q-diet alone or water control;and B) by treating transgenic phosphatase and tensin homolog deleted on chromosome 10 (PTEN) knock out mice with GT alone, Q alone and GT+ Q together using the concentration shown to be most effective for SCID mice. Lack of the tumor suppressor PTEN in the mouse prostate recapitulates many of the pathological features of CaP development in humans. To determine the chemopreventive activity we will measure tumor weight and volume, tumor stage, and cell proliferation, apoptosis by immunohistochemistry. Tumor tissue will be used to measure COMT and 5- cytosine DNA methyltransferase 1 (DNMT1) enzyme activity as well as protein and gene expression using Western blot and quantitative real-time PCR. Multidrug resistance proteins (MRP) may play a role in the increase in bioavailability of EGCG by co-treatment with quercetin. Therefore we will also determine protein and gene expression of MRP1 and MRP2 in tumor tissue. The effect on bioavailability will be determined by analysis of tea polyphenols, quercetin and their metabolites in tumor tissue, liver, lung, and kidney by high performance liquid chromatography and coularray electrochemical detection. This novel combination of natural complementary and alternative agents utilizes the ability of quercetin to reduce the methylation of GTPs and increase their bioavailability at the same time. This novel treatment will retain the non-toxic character of green tea and at the same time increase its activity in chemoprevention of CaP.